The theory of wave propagation in elastic materials is well known and has been used for many years in the analysis and synthesis of seismic records. However, real materials in subterranean formations are rarely purely elastic. They are attenuative and dispersive. The attenuation is seen in the change in amplitude of the travelling wave and in the values of the reflection coefficients. The dispersion contributes to the distortion of the recorded seismic events when compared to the clear predictions of the elastic theory. These effects can be compensated if the appropriate values of the velocities and attenuations can be obtained.
Seismic velocity and attenuation depend on many rock properties including minerology, porosity and microstructure. Accordingly it is important to be able to measure velocity and attenuation in core samples taken from the materials of the subterranean formations. A core sample may be positioned between transmitting and receiving transducers and the travel time of ultrasonic (50 khz--10 Mhz) energy through the core sample measured and the waveform recorded for attenuation analysis.
The transmitting transducer is connected to a pulser to generate ultrasonic energy pulses for travel through the core sample. The receiving transducer is connected to an amplifier to increase the received voltage for recording and velocity and attenuation analysis. This is referred to as the "through transmission " technique.
An alternate technique is the "pulse-echo" technique in which a single transducer is utilized alternately in the transmit and receive modes. In this technique the ultrasonic energy pulse travels from the transducer through the core sample until it is reflected from the interface provided by the opposite end of the sample and returns to the sending end of the sample where the transducer, now in the receive mode, detects the returned energy pulse.